In harmony with the downsizing of electronic equipment, a rapid progress is recently made toward higher integration of LSIs. For LSI mounting, multi-pin thin-film packaging of flip-chip type or the like is employed. To construct such multi-pin structures, the technology for forming bump electrodes of 10 to 100 μm or higher as the connecting terminal is necessary. While a thick resist film is used in forming bump electrodes, it is required that the resist film have a higher sensitivity and be developed in a shorter time. To meet such requirements, Patent Document 1 proposes to add an alkali-soluble resin comprising hydroxystyrene units to a chemically amplified positive resist composition.
Typically, the chemically amplified positive resist composition contains a normally alkali-insoluble polymer adapted to increase its solubility in alkaline aqueous solution under the action of acid as a base resin. When an alkali-soluble resin is added thereto, it is important that there is no substantial difference between the dissolution rate of the normally alkali-insoluble polymer which has turned alkali soluble and the dissolution rate of the alkali-soluble resin. For example, when an alkali-soluble resin comprising hydroxystyrene units having an inadequate dissolution rate is added to the chemically amplified positive resist composition described in Patent Document 2, small pocks known as “dimples” are generated in pattern sidewalls due to a substantial difference of alkaline dissolution rate between the base resin and the alkali-soluble resin.